Not too sure about the short supply rumour, where it stems from and what the motive behind it is ( well ok, I know the motive )
But judging by the mailbox full of leaflets with flats for sale/rent every few days, and looking at the empty units in TC and DB, and looking at the time some places are taking to sell, I question any shortage.
When people line up outside a place ( as in Melbourne, Sydney and Perth ) to rent it and get in a bidding war, that's a shortage, I have not seen this in HK.